A. Field of the Invention
This invention relates to the art of pigment dispersion, and more particularly to high-speed pigment dispersion, and even more particularly to high-speed pigment dispersion without the use of a resin or milling equipment.
B. Description of the Related Art
The batch manufacture of paint products has invariably been restricted by the ability to disperse or grind pigment into a usable state and consistency before finishing the batch with the remaining ingredients or letdown.
The present standard method of pigment dispersion is accomplished in one of the following methods.
1. Mill Dispersion:
                The types of milling methods are varied. The typical methods involve combining a pigment with resins and surfactants in a paste form and subjecting the “paste” to the milling process. The milling apparatus generally subjects the paste to mechanical grinding by passing it through grinding media of some sort.2. High Speed Dispersion:        This method utilizes the same resin/pigment paste as the milling dispersion method described above. The primary difference is the use of high speed mixing equipment as a method of separating pigment particles to achieve final grind specifications. The pigments that can disperse in this method are very limited for color. Deep rich color tones are rarely achieved.3. Base Intermix Tinting:        Base intermixing involves the mixing of clear “non-pigment” components of a paint formula with pre-dispersed pigments that are purchased or manufactured on site. The resultant product is simpler to make on a per batch basis, but tends to be expensive and is frequently subject to specification variation dependant on the type and quantity of colorant used. An additional drawback in this method of making paint is the addition of the binder and additives that are present in the shading paste inherently detract from the product end performance by dilution of the tint base properties.        
The common drawback to all the above is the work involved in the milling or dispersion process. The resins and additives that are utilized in order to mill the pigments are not universally compatible. This results in shading pastes to be purchased in from outside sources. These pastes are expensive and consequently prohibitive economically.
The second drawback to grinding pigments is the batch size restrictions. In order to have an “effective” grind, the batch must be sized to the mill (or tank in the case of hi-speed dispersion). This restricts the paint manufacturer to the batch sizes based on equipment efficiency. Operations must continuously juggle batches as well as equipment based on the ever-changing needs of customers.
Small batch production is non-productive and cost prohibitive because it is labor intensive. It has become such a volatile issue that many gallons and dollars worth of business are passed by each day because of the lack of effective small batch processing.
With reference now to FIGS. 1-3, the manufacture process of pigments results in agglomerates of the pigment by hydrophilic aggregation due to the drying process. To maximize the properties of the pigments, these aggregates have to be further dispersed in the coating manufacturing process to yield desired color strength, opacity, and specular 60%-20% gloss ranges. To achieve this by conventional methods, a resin disperses the pigments to interstitially coat the agglomerates; further, a wetting agent is introduced to wet out the pigment particles composing the aggregates. Finally, through some form of mechanical high shear milling equipment, the pigment aggregate sizes are reduced, creating an increased surface area of the pigment particles. This allows the wetting agent to adsorb onto the surface, blocking reagglomeration.
The classifications of wetting or dispersing agents are primarily categorized into the following three groups in response to charging pigment particles: 1) An anionic acidic wetter is used in compounding pigment with negative charge; 2) A cationic, which is more basic; and 3) an amphoteric resultant salt. Non-ionic dispersants, due to being mechanically basic wetters, will not be discussed.
Conventional milling of a polymer (resin), along with a solvent carrier is required to physically wet out the surface areas of the pigment. Secondly, a dispersant is used to chemically break up Van der Waals force's interaction between the pigment particles in the aggregate accretions. Finally, mechanically, milling equipment is used for high shear and impact to reduce the aggregate sizes. This creates a cost in the milling process due to the loss of grind paste remaining in the mill during transfer. Additionally, to clean for the next production batch, additional solvent and/or resin are used to flush the milling equipment clean.
During formulation for conventional milling it is important to utilize, pigment volume concentration (PVC) & PVC vs. critical pigment volume concentration (CPVC). PVC is the percent pigment by volume correlated to the percent resin by volume. Various pigments, due to chemical and physical properties, have ideal PVC's in a particular resin that must be derived mathematically. CPVC is the PVC point at which the volume of nonvolatile resin portion is maximized to completely coat the pigment surfaces and fill the void spaces between pigment particles. The formula for calculated PVC is PVC=P/(P+V), where P is volume of pigment and V is volume of vehicle. CPVC is calculated by CPVC=[(P/(P+x+y)]×100, where P is volume of pigment, x is volume of adsorbed vehicle, y is volume of void spaces, and V is volume of vehicle.
The present invention provides a new and improved pigment dispersion system and process that does not use resin or milling equipment, and overcomes certain difficulties inherent in the related inventions while providing better overall results.